I concurr. It would be foolish with an opportunity like this not to have the favourite/biggest trilogy characters in an all-out future battle.

I don't think the future should be depandant on the events of TLS. The smartest thing to do is side-step the film entirely by making it clear that the future segments are a "possible" future. This can allow every audience member to come to their own conclusions. There's enough seeds planted in TLS to justify every character's return if you please, and no direct references for those who want to avoid the film like a plague. If nothing is directly addressed, everybody wins, and this film is shed the weight of convoluted previous continuity.